Axial stage injection dual frequency resonator for a combustor of a gas turbine engine

ABSTRACT

A gas turbine engine ( 202 ) including a secondary fuel stage ( 218 ) which also functions as a dual frequency resonator. The engine includes a combustor ( 210 ) and a casing ( 205 ) enclosing the combustor to define a volume ( 214 ). The secondary fuel stage includes a nozzle ( 217 ) sized to be effective as a transverse resonator at a high frequency. The nozzle and the volume ( 214 ) of the casing are sized to be effective as a longitudinal resonator at an intermediate frequency.

STATEMENT REGARDING FEDERALLY SPONSORED DEVELOPMENT

Development for this invention was supported in part by Contract No.DE-FC26-05NT42644, awarded by the United States Department of Energy.Accordingly, the United States Government may have certain rights inthis invention.

FIELD OF THE INVENTION

The invention relates to gas turbine engines, and more particularly to aresonator used to dampen resonance frequencies in a combustor of a gasturbine engine.

BACKGROUND OF THE INVENTION

A conventional combustible gas turbine engine includes a compressorsection, a combustion section including a plurality of can-annularcombustor apparatuses, and a turbine section. Ambient air is compressedin the compressor section and directed to the combustor apparatuses inthe combustion section. FIG. 1 illustrates a conventional combustor 10.As illustrated in FIG. 1, it is known that injecting fuel at two axiallyspaced apart fuel injection locations, i.e., via an upstream fuel stage16 associated with a main combustion zone and a secondary fuel stage 18downstream from the main combustion zone, reduces the production ofNO_(x) by the combustor 10. For example, if a significant portion offuel is injected at the secondary fuel stage 18, the amount of time thatsecondary combustion products are at a high temperature is reduced ascompared to first combustion products, created by the fuel injected bythe upstream fuel stage 16.

FIG. 2 illustrates another conventional combustor 110. During engineoperation, acoustic pressure oscillations at undesirable frequencies candevelop in the combustor 110 due to, for example, burning ratefluctuations inside the combustor 110. Such pressure oscillations candamage components in the combustor 110. To avoid such damage, one ormore damping devices, such as a resonator 124, can be formed byattaching a resonator box 126 to an outer peripheral surface 128 of thecombustor liner 122. As illustrated in FIG. 2, a plurality of resonators124 can be aligned circumferentially about the liner 122. The resonators124 can be tuned to provide damping at a single transverse frequency.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in the following description in view of thedrawings that show:

FIG. 1 is a cross-sectional side view of a conventional combustor usedin a gas turbine engine;

FIG. 2 is a side view of a conventional combustor used in a gas turbineengine;

FIG. 3 is a cross-sectional side view of a gas turbine engine;

FIG. 4 is a cross-sectional side view of a resonator located at adownstream secondary fuel injection location of a combustor;

FIG. 5 is a cross-sectional side view of a resonator located at adownstream secondary fuel injection location of a combustor;

FIG. 6 is a cross-sectional side view of a resonator located at adownstream secondary fuel injection location and a downstream third fuelinjection location of a combustor;

FIG. 7 is a cross-sectional end view of the resonator of FIG. 4; and

FIG. 8 is a plot of a frequency response function versus frequency forthe resonator of FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

The present inventors have recognized several limitations of theconventional resonator that is used to dampen pressure oscillationswithin a combustor of a gas turbine engine. For example, the inventorsrecognized that conventional resonators in a combustor take the form ofadditional components beyond those that are needed to direct and combustfluid in the combustion chamber. Based on this recognition, the presentinventors developed a resonator using the existing components thatdirect and combust fluid in the combustion chamber, and thus eliminatedthe need for additional components.

The present inventors also recognized that conventional resonators in acombustor are limited to dampening one resonant frequency mode, perresonator design. Based on this recognition, the present inventorsdeveloped a resonator for a combustor, which simultaneously dampens ahigh frequency transverse mode and an intermediate frequencylongitudinal mode, thereby reducing the number of required resonatordesigns to dampen multiple resonant frequency modes.

FIG. 3 illustrates a gas turbine engine 202 including a compressor 204that generates compressed air which is passed through a diffuser 207 andinto a casing 205 with a volume 214. The compressed air then enters acan-annular combustor 210, where the compressed air is mixed with a fuelfrom a primary fuel stage and is ignited. As illustrated in FIG. 3, thecasing volume 214 encloses the combustor 210. A secondary fuel line 234is directed to a secondary fuel stage 218 of the combustor 210, toinject fuel into the air/fuel mixture within the combustor 210 at thesecondary fuel stage 218. Additionally, compressed air is injected intothe combustor 210 at the secondary fuel stage 218. The ignited air/fuelmixture is subsequently passed to a turbine 206, to perform work, suchas rotating a shaft 208 connecting the compressor 204 and the turbine206, for example. As illustrated in FIG. 3, the combustor 210 includes aresonator 200 at the secondary fuel stage 218, to dampen multiplefrequencies corresponding to resonant frequency modes of the combustor210, as described below.

FIG. 4 illustrates the resonator 200, which includes the combustor 210and a flow sleeve 212 that encloses the combustor 210. As furtherillustrated in FIG. 4, the combustor 210 includes the secondary fuelstage 218 located at a downstream secondary fuel injection location 246.The secondary fuel line 234 is located at the secondary fuel stage 218and includes an outlet 236 positioned to inject fuel into an inlet 238of a nozzle 217 to deliver fuel to a combustion chamber 240 of thecombustor 210 through the nozzle 217.

Each nozzle 217, by itself, is sized to be effective as a transverseresonator, to dampen a transverse frequency corresponding to a resonanttransverse mode combustion-induced vibrations of the combustor 210. Inan exemplary embodiment, as illustrated in FIG. 4, a length 220 of thenozzle 217 is sized such that the nozzle is effective as the transverseresonator. In an exemplary embodiment, a ratio of the nozzle length tonozzle diameter may be in a range of 0.5-5.0, for example. However, theratio of nozzle length to nozzle diameter is not limited to any specificrange. In an exemplary embodiment, the nozzle 217 acts as a half-waveresonator in a transverse dimension, such that the length 220 is sizedin order for an integral number of half-wavelengths of a transversefrequency to fit along the length 220, where the transverse frequencycorresponds to a resonant transverse mode of the combustor 210. Inanother exemplary embodiment, as illustrated in FIG. 4, the nozzle 217defines an opening 222, and a cross-sectional width 221 of the opening222 is sized such that the nozzle is effective as the transverseresonator. In an exemplary embodiment, a ratio of the nozzle diameter tocombustor diameter may be in a range of 0.01-0.1, for example. However,the ratio of the nozzle diameter to combustor diameter is not limited toany specific range. In another exemplary embodiment, the cross-sectionalwidth 221, in addition to the nozzle length 220 and a volume within thenozzle 217 are sized such that the nozzle is effective as the transverseresonator. FIG. 5 illustrates an alternate resonator 200′ with a nozzle217′ that is located at the downstream secondary fuel injection location246 of the combustor 210. As illustrated in FIG. 5, the nozzle 217′defines a conical opening 222′ with a reduced cross-sectional width 221′toward an outlet 226′ of the nozzle 217′. In an exemplary embodiment,the conical opening may be angled within a range of 75-90 degrees, forexample. However, the angle of the conical opening is not limited to anyspecific range. Although FIGS. 4-5 illustrate nozzles with cylindrical(FIG. 4) and conical (FIG. 5) shaped cross-sectional areas, theembodiments of the present invention is not limited to thesearrangements and the nozzles may have any cross-sectional areaarrangement, provided that the cross-sectional area is such that thenozzle is effective as the transverse resonator. In an exemplaryembodiment, the nozzle 217 is sized to dampen a transverse frequency ina range of 2900-2950 Hz, for example, which corresponds to a resonanttransverse mode of the combustor 210. However, this transverse frequencyrange is merely exemplary and the resonator of the present invention isnot limited to dampening any specific transverse frequency range, sincethe design parameters (i.e. length, cross-sectional area, shape, volume,number of nozzles, etc) of the resonator nozzle can be adjusted suchthat the resonator dampens any desired transverse frequency range. In anexemplary embodiment, the number of nozzles 217 at the secondary fuelstage 218 may be within a range of 8-12 nozzles, for example. However,this range is merely exemplary and any number of nozzles may be used atthe secondary fuel stage 218, provided that the resonator is effectiveas a transverse resonator.

The combination of the nozzle 217 and the casing volume 214 (FIG. 3) areeffective as a longitudinal resonator, and the nozzle 217 and the volume214 are sized in order for the longitudinal resonator to dampen alongitudinal frequency corresponding to a resonant longitudinal mode ofthe combustor 210. In an exemplary embodiment, the longitudinalfrequency dampened by the longitudinal resonator may depend on thecasing volume and/or on a longitudinal dimension within the casingvolume, depending on the geometry of the casing and the target resonantlongitudinal mode to be dampened. In an exemplary embodiment, thelongitudinal frequency dampened by the longitudinal resonator may dependon a combination of the casing volume and the sum of all of nozzleswithin each combustor. In an exemplary embodiment, the casing volume 214acts as a cavity and the nozzles 217 act as a neck of a Helmholtzresonator, for example. In order to be effective as the longitudinalresonator, the quantity of the nozzles 217 may be adjusted. In anexemplary embodiment, the number of nozzles 217 at the secondary fuelstage 218 may be within a range of 8-12 nozzles, for example. However,this range is merely exemplary and any number of nozzles may be used atthe secondary fuel stage 218, provided that the resonator is effectiveas a longitudinal resonator. In an exemplary embodiment, the nozzle 217and the casing volume 214 are sized to dampen a longitudinal frequencyin a range of 50-150 Hz, for example, which corresponds to a resonantlongitudinal mode of the combustor 210. However, this longitudinalfrequency range is merely exemplary and the resonator of the presentinvention is not limited to dampening any specific longitudinalfrequency range, since the parameter (i.e. number of nozzles) of theresonator nozzle and the volume of the casing can be adjusted during adesign phase such that the resonator dampens any desired longitudinalfrequency range.

FIG. 6 illustrates an alternate combustor 200″ including the nozzle 217positioned at the secondary fuel stage 218, as with the combustor 200 ofFIG. 4 discussed above. As with the combustor 200 of FIG. 4, the nozzle217 of the combustor 200″ is sized to be effective as a transverseresonator at a first frequency that corresponds to a first resonanttransverse mode of the combustor 210. However, the combustor 200″further includes a third fuel stage 254 at a downstream third fuelinjection location 252 that is downstream of the second fuel stage 218at the downstream secondary fuel injection location 246. The combustor200″ includes a second nozzle 219″ at the third fuel stage 254 that issized to be effective as a transverse resonator at a second frequencythat corresponds to a second resonant transverse mode of the combustor210, where the second frequency is different than the first frequencyand the second resonant transverse mode is different than the firstresonant transverse mode. The second nozzle 219″ does not extend beyondan inner diameter of the combustion liner wall 230 of the combustor 210.In contrast, the nozzle 217 extends beyond the inner diameter of thecombustion liner wall 230. Although FIG. 6 depicts the first nozzle 217positioned at the secondary fuel stage 218 and extending beyond theinner diameter of the combustion liner wall 230, and the second nozzle219″ positioned at the third fuel stage 254 and not extending beyond theinner diameter of the combustion liner wall 230, this arrangement ismerely exemplary, and the nozzles at each of the second and third stagesmay all extend beyond the inner diameter of the combustion liner wall ormay all not extend beyond the inner diameter of the combustion linerwall, or some combination thereof, for example. Additionally, althoughFIG. 6 depicts that one nozzle may be arranged at a secondary fuel stageand one nozzle may be arranged at a third fuel stage downstream of thesecondary fuel stage, this is merely exemplary, as more than one nozzlemay be arranged at each of the secondary or third fuel stages, and oneor more nozzle(s) may be arranged at additional fuel stages downstreamof the third fuel stage, for example. In an exemplary embodiment, thenumber of nozzles that are arranged at each of the second and third fuelstages may be within the range of 8-12 nozzles, for example. However,this range is merely exemplary and any number of nozzles may be used ateach of the second and third stages, provided that the resonator iseffective as a transverse resonator.

FIG. 7 illustrates an end view of the resonator 200 of FIG. 4 at thedownstream secondary fuel injection location 246 and a plurality ofnozzles 217, 219 arranged at the secondary fuel stage 218. The nozzles217, 219 are arranged at the downstream second fuel injection location246 with an angle 228 between adjacent nozzles 217, 219 in a planetransverse to the combustor longitudinal axis. In an exemplaryembodiment, the angle 228 is selected such that the nozzles 217, 219 areeffective as transverse and longitudinal resonators. In an exemplaryembodiment, the angle may be within a range of 15-90 degrees, forexample. However, the angle is not limited to any specific range. In anexemplary embodiment, the angle may be determined based on the specifictransverse mode that needs to be dampened, for example. Although FIG. 7illustrates two nozzles 217, 219 arranged at the secondary fuel stage218, the embodiment of the present invention is not limited to thisnumber of nozzles and any plurality of nozzles may be arranged at thesecondary fuel stage, provided that the angle between adjacent nozzlesis sized such that the nozzles are effective transverse and longitudinalresonators.

In an exemplary embodiment, the nozzles 217, 219 at the secondary fuelstage 218 may be individually sized (i.e. length, cross-sectional area,etc.) such that a first nozzle 217 is effective as a transverseresonator at a first frequency and a second nozzle 219 is effective as atransverse resonator at a second frequency that is different than thefirst frequency. For example, the nozzles 217, 219 may have differentlengths and/or different cross-sectional areas, such that the nozzle 217and the nozzle 219 are sized to be effective as transverse resonators ata respective first and second frequency. Although the above examplediscusses that two nozzles at the secondary fuel stage may be sizeddifferently to be effective transverse resonators at two distinctfrequencies, the embodiment of the present invention is not limited tothis arrangement, and includes any plurality of nozzles at the secondaryfuel stage being sized differently, to be effective transverseresonators at a plurality of distinct frequencies, for example.Additionally, the length and cross-sectional areas of the nozzles 217,219 may be sized, in addition to the casing volume 214, to ensure thatthe desired longitudinal frequency is dampened.

FIG. 8 depicts a plot of the frequency response function (FRF) of theresonator 200 for a range of frequencies during operation of thecombustor 210. As illustrated in FIG. 8, the resonator 200 is effectiveto simultaneously dampen a transverse frequency 242 corresponding to aresonant transverse mode of the combustor 210 and to dampen alongitudinal frequency 244 corresponding to a resonant longitudinal modeof the combustor 210. The transverse frequency 242 dampened by thenozzle 217 corresponds to a high frequency mode with a range ofapproximately 2900-2950 Hz, and is based on the sizing characteristics(i.e. length, opening, cross-sectional area, etc) of the nozzle 217. TheFRF 248 of the resonator 200 at the transverse frequency 242 is based onthe combination of the individual dampening effects of each nozzle 217at the secondary fuel stage 218. Although the transverse frequency 242discussed above lies within a sample range of 2900-2950 Hz, this rangeis merely exemplary, may include a wider range of 1200-4500 Hz and theembodiments of the present invention is not limited to these ranges andmay include any resonant transverse mode of the combustor, provided thatthe nozzles can be sized to dampen the transverse frequencycorresponding to the resonant transverse mode.

As further illustrated in FIG. 8, the longitudinal frequency 244 is anintermediate frequency mode with a range of approximately 50-150 Hz. TheFRF 250 of the resonator 200 at the longitudinal frequency 244, and therange of the longitudinal frequency mode 244, are based on the volume214 of the casing 205 in combination with the characteristics of thenozzles 217, 219 in each combustor 210 of the engine 202. The number ofnozzles 217 at the secondary fuel stage 218 may affect the longitudinalfrequency 244, such as the center frequency within the range of thelongitudinal frequency 244, for example. Although the longitudinalfrequency mode 244 discussed above lies within a sample range of 50-150Hz, this range is merely exemplary, may include a wider range of 50-400Hz and the embodiments of the present invention is not limited to theseranges and may include any resonant longitudinal mode of the combustor,provided that the casing volume and the nozzles are sized to dampen thelongitudinal frequency corresponding to the resonant longitudinal mode.

In the above embodiment, the resonator 200 dampens a wider range of thelongitudinal frequency 244 (100 Hz) than the range of the transversefrequency 242 (50 Hz). Since the range of the dampened transversefrequency 242 for each nozzle design is relatively narrow, more than onenozzle design may be employed in the resonator, to increase the totalrange of dampened transverse frequencies. As previously discussed,multiple nozzle designs may be provided, where each nozzle design isconfigured to dampen a respective transverse frequency range.

While various embodiments of the present invention have been shown anddescribed herein, it will be obvious that such embodiments are providedby way of example only. Numerous variations, changes and substitutionsmay be made without departing from the invention herein. Accordingly, itis intended that the invention be limited only by the spirit and scopeof the appended claims.

The invention claimed is:
 1. A gas turbine engine comprising: acombustor; a casing enclosing the combustor and defining a volume; and asecondary fuel stage for delivering fuel to the combustor; wherein thesecondary fuel stage comprises a nozzle sized to be effective as atransverse resonator; and wherein the nozzle and the volume of thecasing are configured to be effective as a longitudinal resonator. 2.The gas turbine engine of claim 1, wherein a length of the nozzle isselected to damp vibrations of a selected frequency.
 3. The gas turbineengine of claim 1, wherein the nozzle defines an opening, and wherein across-sectional width of the opening of the nozzle is selected to dampvibrations of a selected frequency.
 4. The gas turbine engine of claim3, wherein the nozzle is conical with a reduced cross-sectional widthtoward an outlet of the nozzle.
 5. The gas turbine engine of claim 1,wherein a plurality of nozzles are arranged at the secondary fuel stageand wherein an angle between adjacent nozzles in a plane transverse to alongitudinal axis of the combustor is selected so that the secondaryfuel stage is effective to damp a selected transverse vibration mode. 6.The gas turbine engine of claim 1, wherein the secondary fuel stagecomprises a first nozzle sized to be effective as a transverse resonatorat a first frequency and a second nozzle sized to be effective as atransverse resonator at a second frequency different than the firstfrequency.
 7. The gas turbine engine of claim 1, wherein the secondaryfuel stage comprises a first nozzle sized to be effective as atransverse resonator at a first frequency and wherein a third fuel stagedownstream of the secondary fuel stage comprises a second nozzle sizedto be effective as a transverse resonator at a second frequencydifferent than the first frequency.
 8. The gas turbine engine of claim1, wherein the nozzle extends beyond an inner diameter of a combustionliner wall of the combustor.
 9. The gas turbine engine of claim 1,wherein the nozzle does not extend beyond an inner diameter of acombustion liner wall of the combustor.
 10. The gas turbine engine ofclaim 1, wherein a ratio of a length to a diameter of the nozzle is in arange of 0.5-5.0.
 11. The gas turbine engine of claim 1, wherein a ratioof a diameter of the nozzle to a diameter of the combustor is in a rangeof 0.01-0.1.
 12. In a gas turbine engine comprising a casing defining avolume enclosing a combustor, a resonator located at a downstreamsecondary fuel injection location of the combustor, said resonatorcomprising: a fuel line outlet positioned to inject fuel into an inletof a nozzle effective to deliver fuel to the combustor through thenozzle; wherein the nozzle is configured to be effective as a transverseresonator for transverse vibrations in a range of 1200-4500 Hz; andwherein the nozzle and the volume of the casing enclosing the combustorare configured to be effective as a longitudinal resonator forlongitudinal vibrations in a range of 50-150 Hz.
 13. The resonator ofclaim 12, wherein a ratio of a length to a diameter of the nozzle is ina range of 0.5-5.0.
 14. The resonator of claim 12, wherein a ratio of adiameter of the nozzle to a diameter of the combustor is in a range of0.01-0.1.
 15. The resonator of claim 12, wherein a plurality of nozzlesare arranged at the downstream secondary fuel injection location andwherein an angle between adjacent nozzles in a plane transverse to alongitudinal axis of the combustor is selected so to damp a selectedtransverse vibration mode.
 16. The resonator of claim 12, wherein thenozzle extends beyond an inner diameter of a combustion liner wall ofthe combustor.
 17. The resonator of claim 12, wherein the nozzle doesnot extend beyond an inner diameter of a combustion liner wall of thecombustor.
 18. In a gas turbine engine comprising a casing defining avolume and a can-annular combustor disposed within the casing volume,the improvement comprising: a plurality of nozzles formed in a wall ofthe combustor to define a secondary fuel injection location; a fueloutlet disposed proximate an inlet of each nozzle for delivering asecondary fuel into the combustor through the nozzles; wherein thenozzles are configured to be effective as a resonator to dampen atransverse frequency mode of pressure oscillations developed within thecombustor during operation of the engine; and wherein the nozzle and thecasing volume are jointly configured to be effective as a resonator todampen a longitudinal frequency mode of the pressure oscillations. 19.The gas turbine engine of claim 18, further comprising a first of thenozzles configured differently than a second of the nozzles to beeffective at different respective frequencies.
 20. The gas turbineengine of claim 18, further comprising: wherein the nozzles areconfigured to be effective to damp transverse vibrations in a range of1200-4500 Hz; and the nozzles and the casing volume are configured to beeffective to damp longitudinal vibrations in a range of 50-150 Hz.